The long-term objective of this proposal is to study the psycho-biological phenomena of hunger, satiety, taste and eating behavior in patients with the eating disorders of Anorexia Nervosa (AN) and Bulimia Nervosa (BN). Investigation of the interaction between psychological-behavioral and metabolic conditions pertaining to eating behavior in eating disorder patients should provide salient information for more effective clinical interventions that are currently available. The major general hypotheses of this research is that analyses of the processes of hunger and satiation during manipulation of contextual variables, such as the macronutrient (fat, carbohydrate, protein) content of food will reveal distinguishing differences between the eating disorder subgroups and control persons. These differences in the processes of hunger and satiation will reflect underlying physiological mechanisms, eg. neurotransmitters and hormones, that are involved in regulating eating. The effect of macronutrient manipulations in meals on the perceptions of hunger and satiety and on the microstructure of eating behavior will be studied by 1. examining total calorie intake, sequence of macronutrient intake, relationship of taste preference to macronutrient intake, type of fats and carbohydrates, 2. examining perceptions of hunger and satiety during meals and preloads, 3. examining the cognitive sets by assessing attitudes (preferences, emotions) towards foods containing different proportions of macronutrients. The relationship of the processes of hunger and satiety to serotonin function (a well-known physiological regulation of eating behavior) will be analyzed. Serotonin, a neurotransmitter which facilitates satiety, will be studied in eating disorder and control persons by the fenfluramine challenge test, analysis of serotonin platelet receptors and serotonin provoked platelet aggregation.